Corrugator



W. A. NIKKEL Nov. 16, 1965 CORRUGATOR 3 Sheets-Sheet 1 Filed Sept. 25, 1962 INVENTOR. WILLEM A. NIKKEL AGENT W. A. NIKKEL Nov. 16; 1965 GORRUGATOR 3 Sheets-Sheet 2 Filed Sept. 25, 1962 INVENTOR. WILLEM A. NIKKEL BY what-0M 3. W AGENT Nov. 16, 1965 w. A. NIKKEL 3,217,425

CORRUGATOR Filed Sept. 25, 1962 3 Sheets-Sheet s INVENTOR. WILLEM A. NIKKEL BY wbwwwlww AGENT United States Patent 3,217,425 CORRUGATOR Willem A. Nikkei, Covington, Va, assignor to West Virginia Pulp and Paper Company, New York, N.Y., a corporation of Delaware Filed Sept. 25, 1962, Ser. No. 226,037 9 Claims. (Cl. 3449) This invention relates generally to improvements in a corrugator and particularly to improvements in the double backer of a corrugator.

The manufacture of corrugated board generally begins with apparatus referred to in the industry as a single facer. The single facer forms the corrugated medium and adhesively joins the peaks of the flutes of the corrugated medium to a liner. The corrugated medium is usually manufactured in the single facer by running a suitable paper web through the nip of meshing gear-like corrugating rolls that impart the corrugated shape to the paper web by forcing the web to conform to the corrugated surfaces of the rolls.

The corrugated medium is usually combined with the liner in a nip formed by one of the corrugating rolls and a smooth surfaced roll. The corrugated medium travels in the contour of the corrugating roll to the nip created by the smooth surface roll where only the peaks of the flutes contact the liner. High pressure and temperature are exerted in the nip to set the adhesive quickly, forming a bond that holds the corrugated medium to the liner and allowing the operation of the single facer to be carried out in a relatively short distance. The single facer, as a result, requires little space.

The single faced board travels to apparatus referred to in the industry as a double backer where the exposed side of the corrugated medium is adhesively combined with a second (outside) liner to form double face board. In the past, the double backer has formed a long and expensive portion of the corrugator. Appreciably less pressure can be exerted in the double backer to set the adhesive bond between the single faced board and the outside liner. High pressure will flatten the flutes of the corrugated medium because it is not possible to support the corrugated medium directly as is the case in the single facer where a backing surface is formed by the corrugating roll.

The reduction of allowable pressure in the double backer causes the adhesive applied to unite the outside liner with the single faced board to set considerably slower than the adhesive applied in the single facer to unite the corrugated medium with the liner to form the single faced board. The overall effect is an increase in the time necessary for the adhesive to set in the double backer as compared with the single facer. The additional time is physically apparent as additional length in the double backer. As corrugator speeds have increased, lengths of 90 feet or more in the double backer have been reached. Many attempts have been made to shorten the length of the double backer by increasing the efiiciency of the heat transfer from the heat source to the double faced board. My invention, through a novel arrangement of and use of components, has greatly reduced the length of the double backer by increasing the heat transfer efficiency.

An efficient means of controlling warp in the double faced board is also incorporated into the double backer. The phenomenon of warp is dependent upon and varies with differences of moisture content in the liners that form the double faced board. A liner containing more initial moisture shrinks more upon drying than a liner containing less initial moisture. The end effect is a curvature or warpage of the double faced board.

The usual procedure to correct Warp is to visually inspect the double faced board after manufacture and determine the direction of warp. More heat is manually added to the appropriate liner to reduce the moisture content. Partially because manual control was only an approximate solution, the industry has practiced what is commonly referred to as reversed stacking. In reversed stacking, alternate groups of boards are turned over during stacking to prevent a summation of the Warp. The reverse stacking operation is in itself time consuming and costly and is especially bothersome when the corrugators contain apparatus for printing and scoring the double faced board.

The alternate groups of boards have printed and scored sides reversed from the remaining groups of boards. This situation makes it necessary for the ultimate user, such as a box manufacturer, to re-sort his supply of corrugated board so that all of the boards have the printed and scored sides again facing in the same direction.

Warp is controlled in the herein disclosed double backer so that the reversed stacking and the associated resorting is eliminated by carefully controlling the moisture content of the liners.

As mentioned earlier, the double backer as described herein is considerably shorter in length than those now in use because of improvements in the heat transfer efiiciency. The shorter double backer has many advantages, such as conservation of floor space and machinery parts.

Further advantages of the double backer will become apparent from the following detailed description considered in connection with the drawings in which:

FIG. 1 is a side elevational view of the double backer.

FIG. 2 is a cross sectional elevational view taken generally along line 2-2 of FIG. 1.

FIG. 3 is an enlarged fragmentary view taken generally along line 3-3 of FIG. 1 showing internal details of the heat transfer assembly.

FIG. 4 is another view of the heat transfer assembly taken generally along line 44 of FIG. 3 showing other internal details of the heat transfer assembly.

FIG. 5 is an enlarged fragmentary view showing a por tion of the heat transfer assembly of FIG. 4.

FIG. 6 is an enlarged fragmentary view taken generally along line 6-6 of FIG. 1 showing in greater detail a part of the warp controlling apparatus.

FIG. 7 is a cross sectional elevational view taken generally along line 77 of FIG. 1 showing in greater detail yet another part of the warp controlling apparatus.

FIG. 8 is an enlarged fragmentary view showing in greater detail a damper system that forms still another part of the warp controlling apparatus.

FIG. 9 is a schematic circuit diagram of a warp control system used with the warp controlling apparatus shown in FIGS. 6, 7, and 8.

Referring to the drawings, the corrugated board components, in this instance the single faced board 10 and the outside liner 11, traveling in the directions indicated by the arrows, pass through heated air directed thereon by the preheaters 12 and 13, respectively, and through the ingoin nip 14 created by the first pair of superimposed belt rolls 15 and 16. Adhesive is applied to the exposed peaks of the flutes of the single faced board by a suitable glue applicator (not shown) before the two boards travel through the ingoing nip 14. The adhesive applied to the single faced board 10 contacts the outside liner 11 in the ingoing nip 14. A second pair of superimposed belt rolls 17 and 18 are substantially horizontally displaced from the first pair of superimposed belt rolls 15 and 16. A lower endless belt 19 spans the distance between the lower belt rolls 16 and 17 of the first and second pairs of belt rolls, respectively, and an upper endless belt spans the distance between the upper belt rolls 15 and 18 of the first and second pairs of belt rolls, re spectively. The upper reach of the lower endless belt 19 is held substantially planar by idler rollers 21. The lower reach of the upper endless belt 20 is prevented from moving upwardly out of parallelism with the planar upper reach of the lower endless belt 19 by similar idler rollers 22. The planar sections of the endless belts 19 and 20 extend from the ingoing nip 14 to the outgoing nip 23. The lower reach of the lower endless belt 19 and the upper reach of the upper endless belt 20 are supported by suitable rollers 24.

The primary function of the idler rollers 21 and 22 is to transmit a force through the planar reaches of the endless belts 19 and 20, respectively, thereby forming a pressure zone in the area defined by the adjacent reaches of belts 19 and 20 that will hold the single faced board 10 firmly against the outside liner 11 during travel therethrough. The double faced board, hereinafter referred to by the reference numeral 25, is subjected to heated air directed thereon by the air hood 26 during travel between adjacent planar reaches of the lower endless belt 19 and the upper endless belt 20. As will become clearer in the following description, the adhesive sets as the double faced board travels from the ingoing nip 14 to the outgoing nip 23. The double faced board 25 passes from the outgoing nip 23 through warp sensing apparatus 27 that forms a part of the warp control apparatus as will become clearer in the following discussion. The double faced board 25 travels past the warp sensing apparatus 27 and on to other devices, such as slitters, scorers, and cut-off knives. The slitters, scorers, and cut-off knives are not essential components of the double backer designed according to this invention and are not included in the drawings.

The upper and lower endless belts 20 and 19, respectively, are driven by the second pair of superimposed belt rolls 17 and 18 in the direction indicated by suitable means, such as an electric motor 28. A chain 29 connects the electric motor 28 to the lower belt roll 17 of the second pair of superimposed rolls by the sprockets 30 and 31, respectively. The upper belt roll 18 of the second pair of superimposed rolls is driven by an attached gear 32 which meshes with a gear 33 attached to the lower belt roll 17 of the second pair of superimposed belt rolls. The

drive system moves the planar reaches of the endless belts 19 and 20 in the same sense and at an equal speed. The equal speeds of the upper and lower endless belts 20 and 19 combine with the pressure exerted by the idler rollers 21 and 22 to hold the single faced board 10 and the outside liner 11 together without any relative slipping occurring therebetween.

A fan 34 driven by suitable means (not shown) has an outlet 35 connected to a suitable heater which, for the purposes of illustration, is indicated as an electric heater '36. The air forced past the electric heater 36 by the fan 34 is raised in temperature to a suitable value as controlled by suitable means, such as a thermostatic unit (not shown). The heated air from the electric heater 36 flows along the main heating duct 37 and into heating duct branches 38 and 39. The heating duct branch 38 supplies heated air to the air hood 26. The heating duct branch 39 supplies heated air to the preheaters 12 and 13 through the preheater heating ducts 40 and 41, respectively. A main return duct 42 is received by the inlet 43 of the fan 34. A return duct branch 44 brings the air from the preheaters 12 and 13 to the main return duct 42 and a return duct branch 45 brings the air from the air hood 26 to the main return duct 42. A portion of the return duct branch 44 is broken away in FIG. 1 to clearly indicate the location of the heating ducts. The return duct branch 44 is subdivided into a return duct 46 that is connected to the preheater 12 and a return duct 47 that is connected to the preheater 13. The heating duct branch 39 contains flow control means 48 that regulates the flow of heated air to the preheaters 12 and 13. The total flow of heated air through the main heating duct 37 is controlled by a standard system that regulates the flow of heated air to the air hood 26 and to the preheaters 12 and 13 (total circulating air). A fresh air inlet 49 connected to the main return duct 42 near the inlet 43 of the fan 34 supplies makeup air. A clearer understanding of the arrangement of the ducting can be obtained by referring particularly to FIGS. 2 and 6. In FIG. 2, the return duct branch 45 can be seen as extending outside of the heating duct branch 38, and in FIG. 6 the return duct 47 can be seen extending away from the preheater 13 outside of the preheater heating duct 41.

Referring in particular to FIGS. 3 and 4, the return duct branch 45 opens into an exhaust chamber 50 and the heating duct branch 38 opens into one end of a manifold chamber 51. The manifold chamber 51 extends along the length of the air hood 26 and forms a channel for the heated air. The heated air flows in the manifold chamber 51 past passages 52 spaced along one wall thereof. The heated air flowing along the manifold chamber 51 enters the passages 52 and flows into the nozzle chambers 53. The heated air flows along the nozzle chambers 53 and through slots 54 extending across the corrugator in the lower wall of the nozzle chambers 53. Notice from FIG. 4 that the nozzle chambers 53 are closely spaced along the double backer and that heated air issuing from the slots 54 is directed toward the outside liner 11 of the double faced board 25. The heated air contacts the upper surface of the outside liner 11 and is deflected by the upper surface into the exhaust chamber 50. The heated air travels in the exhaust chamber 50 to the return duct branch 45. The internal structure of the air hood 26 is illustrative only, and can be varied in detail without leaving the scope of this invention. Referring in particular to FIG. 5, the air flow is represented by the arrows, and its travel through the slots 54 to the outside liner 11 and back to the exhaust chamber 50 is clearly indicated. The novel use of a belt having an open weave permits the heated air to impinge directly onto the upper surface of the double faced board 25 by flowing through the mesh forming the belt 20. The belt is preferably metallic, but may be made of non-metallic heat resistant materials. The direct impingement may be obtained by using spaced strips of heat resistant material or chain in lieu of the wire mesh belt construction. Any construction that permits direct impingement of heated air upon the upper surface of the outside liner 11 to increase the heat transfer efliciency will perform satisfactorily. Both endless belts 19 and 20 are illustrated in FIG. 5 as having an open wave. It is to be understood that only the upper endless belt 20 need be open weave. No heated air is indicated as flowing through the lower endless belt 19. However, such usage is intended to fall within the scope of this invention. The system thus described allows optimum heat transfer in which the adhesive between the outside liner 11 and the single faced board 10 is raised rapidly to a setting temperature. As a result of the efficient heat transfer, the length of the double backer can be reduced to approximately half of the length of the prior art double backers.

The fresh air inlet 49 contains a damper 55 that regulates the quantity of makeup air introduced into the inlet 43 of the fan 34. Those familiar with the characteristics of hot air heating are well aware that the circulating heated air will pick up moisture only until it becomes saturated. Saturated air cannot remove further moisture from the system. The function of the air system in the double backer of setting the adhesive bond between the outside liner 11, and the single faced board is not appreciably affected when the heated air becomes saturated; however, the warp control apparatus is affected. Relatively dry air must be entered into the system to assure that the circulating heated air is capable of removing additional moisture; i.e., air containing less moisture than that saturated air at the same temperature. If this is not carried out, the moisture in the outside liner 11, and the single faced board 10 cannot be satisfactorily controlled.

The warp control apparatus is particularly pointed out in FIGS. 7, 8, and 9. Two pairs of horizontally displaced rolls 56 and 57 extend from a position beginning at an edge of the double faced board to approximately the center (the pair of rolls 57 is best shown in FIG. 1). The pair of rolls 56 and 57 form nips through which approximately half of the double faced board 25 travels. The nips of the rolls 56 and 57 prevent horizontal movement of that portion of the double faced board 25 traveling therebetween. The pairs of rolls 56 and 57 are rotatably mounted to a side frame 58 and to inside secondary frames 59. The frames separate the top and bottom rolls of the pair of rolls 56 and 57 by a distance substantially equal to the thickness of the double faced board 25. The remaining portion of the double faced board 25 is allowed to float or displace horizontally without restraint.

A warp sensor 60 is rigidly attached by a suitable frame member 61 over the floating portion of the double faced board 25 so that the activating lever 62 rides on the surface thereof. The double faced board 25 is indicated in the normal or warp-free position and as its warps, moves toward one of the positions marked A and B in FIG. 7. When the board is in the warp-free position, the warp sensor 60 sends a signal that has a pre-set strength referred to as the set point signal. As the double faced board warps upwardly to the position referenced by the letter A, the signal from the warp sensor 60 increases from the set point in a proportional manner as determined by the travel of the activating lever 62. On the other hand, as the double faced board 25 warps downwardly toward the position referenced by the letter B, the warp sensor 61?, through the movement of the activating lever 62, sends out a signal which decreases from the set point proportional to the displacement therefrom. A warp sensor 60 that sends a signal decreasing in strength as the double faced board 25 travels toward position A, and a signal increasing in strength as the double faced board 25 warps toward position B will work equally well if the remaining components of the control system are altered to the reversed signal. Referring to FIG. 9, the warp sensor 60 transfers the signal by a control line 63 to a controller 64. The signal from the warp sensor 613 energizes the controller 64 which through line 65 controls the position of the fluid cylinder 66. Controllers such as indicated at 64 that convert a constant fluid pressure input to a varying fluid pressure output are commercially obtainable from most instrument suppliers. In FIG. 9, the fluid input to the controller 64 is obtained from a suitable source (not shown) through the pipe 67. The output of the controller 64 is fed to one end (the blank end) of the fluid cylinder 66 through pipe 65. The pressure in the pipe 65 is controlled by the controller 64 as energized by the signal from the warp sensor 60. Increases in pressure in the pipe 65 extend the fluid cylinder 66, while decreases in pressure in the pipe 65 cause the spring 68 (the spring 68 is schematically represented in FIG. 9, actually forms an internal part of a commercial fluid cylinder) to contract the fluid cylinder 66. This movement is transmitted by the piston rod 69 through the linkage 70 to the damper 71. Linkage 79 is rigidly attached at one end to damper 71 and pivotally attached at its other end to piston rod 69. The damper 71 is rotated about the pivot 72. The particular layout of the fluid cylinder 66, the linkage 70, and the damper 71 is better shown in FIG. 8.

The internal construction of the preheaters 12 and 13 is not pointed out in the drawings. However, the preheaters 12 and 13 are preferably so constructed that they contain means for directing the heated air onto the single faced board 10 and the outside liner 11, respectively, and means for returning the so-directed air back into the circulating air system. The internal details of the air hood 26, as shown in FIGS. 3 and 4, are representative of the internal details of the preheaters 12 and 13. The broken line '73 of FIG. 6 indicates an internal division between an exhaust chamber 74 and nozzle chambers 75 similar to the exhaust chamber 50, and the nozzle chambers 53 of the air hood 26.

In operation, as the double faced board 25 warps upwardly toward position A, the activating lever 62 of the warp sensor 60 travels therewith and causes an increase in the signal to the control line 63 leading to the controller 64. The increase in the signal to controller 64 causes a corresponding increase in the pressure in pipe 65 and brings about an extension of the fluid cylinder 66. The extension of the fluid cylinder 66 to the left as seen in FIGURES 8 and 9 rotates the damper 70 about a pivot 72 in a counterclockwise direction as viewed in FIG. 8. The counterclockwise rotation of the damper 71 reduces the flow of heated air to the preheater heating duct 40 and increases the flow of the heated air through the preheater heating duct 41. Referring in particular to FIG. 1 of the drawings, notice that preheater heating duct 41 sends heated air to the preheater 13 and that the preheater heating duct 40 sends heated air into the air preheater 12. By rotating the damper 71 counterclockwise as the double faced board 25 warps toward position A more heat is added to the outside liner 11, resulting in a reduction of moisture content therein. Since warpage toward position A results from excessive moisture in the outside liner 11 at the time it is joined to single faced board 10, the reduction in the moisture therein before it is joined to single faced board 10 overcomes warpages tendencies in the double faced board.

On the contrary, as the double faced board 25 warps toward position B as shown in FIG. 7, the lever 62 moves downwardly and decreases the signal sent through control line 63 to the controller 64. The controller 64 decreases the pressure in pipe 65 and the fluid cylinder 66 contracts. The contraction of the fluid cylinder 66 rotates the damper 71 about the pivot 72 in a clockwise direction as viewed in FIG. 8. The clockwise rotation constricts the flow of heated air through the preheater heating duct 41 and increases the flow of heated air through the preheater heating duct 40. The increase in flow of heated air through the preheater heating duct 40 increases the amount of heated air directed upon the single faced board 10, which as explained previously, increases the amount of moisture removed therefrom by the preheater 12. At the same time, the reduction in the flow of heated air through the preheater heating duct 41 to the preheater 13 reduces the amount of moisture removed from the outside liner 11. In both cases, the overall effect is a rapid tendency to equalize the moisture contents of these two boards, thus alleviating the warpage as sensed by the warp sensor 60.

The warp control system disclosed in FIGS. 7 and 9 is illustrative of a simple, yet effective means for sensing the occurrence of warp, and means for energizing the preheaters 12 and 13 to adjust the moisture content of the single faced board 10 and the outside liner 11. Numerous substitutes can be found for the disclosed position transmitter (warp sensor 60). A device capable of sensing a movement in the floated portion of the double faced board, and transforming this movement into a proportional signal can become a substitute. Revisions in the other components of the control system can be easily resorted to without leaving the scope of this invention. The preheaters 12 and 13 also function as means to heat the single faced board 10 and the outside liner 11, respectively, and as a result, the temperature of both boards is raised so that the adhesive will set quicker. The control of warp, when combined With the heated air system and the novel open weave construction of the endless belt, provides a double backer of substantially shorter construction and more economical operation. The double faced board 25 produced from a double backer designed according to my invention does not need reverse stacking and, as a result, apparatus such as slitters, scorers, and printers can be combined with the corrugator to form a complete, single unit. The concepts disclosed herein are applicable to other corrugating and laminating equipment. As an example, corrugating equipment manufacturing double Wall or triple wall corrugated board could be easily modified to use the heated air and the warp control systems.

Many modifications can be made to the basic invention disclosed herein, all of which are intended to be included which fall within the scope of the following claims.

I claim:

1. Apparatus of the type described comprising:

(a) A first pair of horizontally extending rolls arranged in vertically stacked, parallel relation forming on ingoing nip,

(c) said first ETAO (b) a second pair of horizontally extending rolls arranged in vertically stacked, parallel relation forming an outgoing nip,

(c) said first pair of rolls extending in spaced parallel relation to said second pair of rolls,

((1) a first endless belt trained around the upper rolls of said pairs of vertically stacked rolls and having substantially planar upper and lower reaches,

(e) a second endless belt trained around the lower rolls of said pairs of vertically stacked rolls and having substantially planar upper and lower reaches,

(f) at least said upper belt being pervious to the passage of heated air therethrough,

(g) said lower reach of said first belt and said upper reach of second belt defining therebetween a pressure zone.

(h) a manifold chamber extending between said upper rolls of said pairs of vertically stacked rolls,

(i) a heating duct in communication with said manifold chamber,

(j) a plurality of nozzle chambers positioned between the upper and lower reaches of said first belt and in communication with said manifold chamber,

(k) said nozzle chambers being adapted to direct heated air through said upper belt toward said pressure zone,

(1) an exhaust chamber overlying said nozzle chambers, and

(m) a return duct in communication with said exhaust chamber.

2. Apparatus as in claim 1 wherein said first endless belt is of open weave, wire mesh construction.

3. Apparatus of the type described comprising:

(a) Means for continuously bonding together in coextensive relationship a plurality of corrugated board components of indefinite length,

(b). means for preheating each of said corrugated board components prior to their assembly,

(c) means for sensing warpage of said corrugated board components subsequent to their assembly and generating signals proportional to said warpage,

((1) means for varying the output of said preheating means, and

(e) means responsive to signals generated by said sens- 8 ing means for controlling said varying means to correct said warpage.

4. Apparatus as defined in claim 3 wherein:

(a) Said preheating means includes a plurality of pre heaters, corresponding in number to said plurality of corrugated board components, and

(b) said varying means includes a damper positioned to vary the flow of heated air through said preheating means.

5. Apparatus as defined in claim 3 wherein said sensing means includes:

(a) Means for contacting said assembled, corrugated board components,

(b) said contacting means being adapted to move in response to deviations of said components from a preselected configuration.

6. Apparatus as defined in claim 5 wherein said signal responsive means includes:

(a) A cylinder, and

(b) a spring loaded piston slidably engaged in said cylinder,

(c) one end of said piston being operatively engaged with said varying means, whereby movement of said piston in response to signals received from said sensing means effects a variation of the output of said preheaters. piston in response to signals received from said 7. Apparatus as defined in claim 6 wherein:

(a) Said preheating means includes a plurality of pre heaters, corresponding in number to said plurality of corrugated board components, and

(b) said varying means includes a damper positioned to vary the flow of heated air through said preheating means.

8. Apparatus for controlling warpage in the manufacture of corrugated board comprising:

(a) means for applying heat and pressure to a plurality of continuous, coextensive, sheet-like, corrugated board components of indefinite length to form a corrugated board,

(b) said means including an ingoing and an outgoing (0) a plurality of preheaters, one for each of said corrugated board components,

(d) said plurality of preheaters being positioned adjacent and prior to said ingoing nip in spaced relation to each other,

(e) a sensing mechanism positioned adjacent and subsequent to said outgoing nip,

(f) said sensing mechanism being adapted to sense warpage in said corrugated board and generate sig nals proportional to the degree of said warpage,

(g) a heat control mechanism for controlling the output of said preheaters,

(h) said heat control mechanism being responsive to signals generated by said sensing mechanism; whereby warpage of said corrugated board will be detected by said sensing mechanism and subsequent warpage obviated through regulation of said preheaters.

9. Apparatus of the type described comprising:

(a) a first pair of horizontally extending rolls arranged in vertically stacked, parallel relation forming an ingoing nip,

(b) a second pair of horizontally extending rolls arranged in vertically stacked, parallel relation, forming an outgoing nip,

(c) said first and said second pairs of rolls extending in spaced, parallel relation to each. other,

(d) a first endless belt trained around the upper rolls of said pairs of vertically stacked rolls and having substantially planar upper and lower reaches,

(e) a second endless belt trained around the lower rolls of said pairs of vertically stacked rolls and having substantially planar upper and lower reaches,

(f) all'of said reaches extending in spaced substantially parallel relationship,

(g) at least said first belt being pervious to the passage of air therethrough,

(h) a heated air conveying hood positioned between the upper and lower reaches of said first belt and directing heated air through the lower reach thereof,

(i) a single faced board preheater upstream of said incoming nip,

(j) an outside liner preheater upstream of said incoming nip and spaced from said single faced board preheater,

(k) a warp sensor downstream of said outgoing nip,

(1) a damper controlling the relative output of said preheaters, and

(m) a control system for controlling said damper in response to indications received by said warp sensor; whereby Warpage in the combined single faced board and outside liner will be sensed by said warp sensor and appropriate signals conveyed to said damper control to regulate the output of said preheaters to prevent further warpage.

References Cited by the Examiner UNITED STATES PATENTS 1/1899 Chapin 156-221 9/1907 Pickles 3449 6/1938 Stanton 3449 12/1938 Olfen 34--54 7/1939 Skagerberg 3454 X 10/1947 Munters 18-19 X 4/1952 Ware et a1 156322 X 11/ 1955 Ehrisman 34--49 8/1956 Goldstein et a1. 156--594 X FOREIGN PATENTS 9/ 1958 Italy.

WILLIAM F. ODEA, Primary Examiner. 20 NORMAN YUDKOFF, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,217,425 November 16, 1965 Willem A. Nikkel It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 43, for "warpages" read warpage column 7, line 30, strike out "(c) said first ETAO"; column 8, line 27, strike out "piston in response to signals received from said".

Signed and sealed this 20th day of September 1966.

(SEAL) Attcst:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer ioner of Patents 

3. APPARATUS FOR THE TYPE DESCRIBED COMPRISING: (A) MEANS FOR CONTINUOUSLY BONDING TOGETHER IN COEXTENSIVE RELATIONSHIP A PLURALITY OF CORRUGATED BOARD COMPONENTS OF INDEFINITE LENGTH, (B) MEANS FOR PREHEATING EACH OF SAID CORRUGATED BOARD COMPONENTS PRIOR TO THEIR ASSEMBLY, (C) MEAN FOR SENSING WARPAGE OF SAID CORRUGATED BOARD COMPONENTS SUBSEQUENT TO THEIR ASSEMBLY AND GENERATING SIGNALS PROPORTIONAL TO SAID WARPAGE, 